1. Field of the Invention
The present invention relates to an effect image processing method which generates an image obtained by viewing an object existing in a virtual three-dimensional space from a predetermined viewpoint in the virtual three-dimensional space, and in particular to an effect image processing method and apparatus for providing an effect processing around an object in a virtual three-dimensional space, and a program for the effect image processing method.
2. Description of the Related Art
In a game apparatus for realizing a computer game such as a so-called action game or role playing game, a hero/heroine (player character) in game pictures displayed on a screen of a display means is controlled and a story of the game is developed in response to an operation signal from an input means (controller pad) operated by a player. In particular, in recent years, following the improvement of a hardware performance, game pictures in which a player character moves in a virtual three-dimensional space are provided by three-dimensional graphics, whereby stage effects of the game is increased.
Three-dimensional graphics determines a relative spatial position of an object, which exists in a direction of a line of sight, from a viewpoint position in a virtual three-dimensional space based upon three-dimensional data representing the object and performs image processing such as rendering processing to represent the object three-dimensionally. That is, in a game utilizing the three-dimensional graphics, a player character and other objects viewed from the viewpoint position are represented three-dimensionally and the viewpoint or a line of sight is changed according to movement of a player or a game scene, whereby game pictures representing the virtual three-dimensional space are provided.
Incidentally, in a game frequently using the three-dimensional graphics such as an action game, an interest of the game often depends upon game pictures represented on a display in addition to a plot of the game. Therefore, in producing a game (game program), a type of game pictures provided to a player is a very important element. In a conventional game, game pictures representing a virtual three-dimensional space from a specific camera angle are provided. For example, game pictures are provided which look as if a player is photographing a character by pursuing the same, which is moving in response to operations of the player, from a virtual camera arranged in an upper rear position of the character. In addition, in the case in which an existing object other than a background in a distant place, for example, fog is represented, an effect image depicting a view of the object is synthesized with an image of the background in the distant place or the character, whereby various objects coming into a visual field of the virtual camera are represented, and the sense of reality is increased.
FIG. 1 schematically shows a method of displaying an effect image in a conventional game apparatus. For example, in the case in which an object existing between a viewpoint of a virtual camera 2 and a player character 1 in a visual field area of the virtual camera 2 is represented, a plane object 3 consisting of a rectangle two-dimensional model is provided as a polygon object for applying a texture image for an effective representation (fog, etc.) in front of the virtual camera 2, and an effect image (the texture image for the effective representation) is applied to the plane object 3 and synthesized with a main image of the player character 1 or the like to display the effect image. Alternatively, a technique is used which provides a large number of small plane objects 4, on which an image for the effective representation is projected, between the virtual camera 2 and the player character 1 as shown in FIG. 2 or arranges a plurality of plane objects 4 putting one behind another to display an effect image.
Here, the conventional image processing method for providing an effect processing around an object will be described more in detail with the case in which an effect processing for representing a pouring rain is provided to pictures, which are obtained by viewing an object 1 in a virtual three-dimensional space from respective viewpoints of virtual camera 2, as shown in FIGS. 3A to 3D as an example. Note that, in FIG. 3A, reference symbol V1 denotes an effect image on which the object 1 is viewed from an upper rear viewpoint; V2, an effect image on which it is viewed from a side viewpoint; V3, an effect image on which it is viewed from an upper front viewpoint; and V4, an effect image on which it is viewed from an upper viewpoint. In a three-dimensional coordinate system as shown in FIG. 3A, three-dimensional coordinates of the object 1 viewed from, for example, the upper, side, and upper front viewpoints are converted into a two-dimensional coordinate system by perspective conversion or the like and represented by shapes shown in FIGS. 3B, 3C, and 3D, respectively. FIGS. 4A, 4B, 4C, and 4D show display effect images of the object 1 and show images V1, V2, V3, and V4 of the object 1 viewed from the respective viewpoints of the virtual camera 2 in FIG. 3A, respectively. Such a conventional image processing method of providing an effect processing to images of an object in a virtual three-dimensional space (hereinafter referred to as an effect image processing method) will be hereinafter described.
FIG. 5 schematically shows a first embodiment of the conventional effect image processing method. In the case in which “rain” is displayed as an effect image by using the above-mentioned rectangle plane object 3 (see FIG. 1), as shown in FIG. 5, plane objects on which effect images E01(b), E02, E03, and E04 are applied are arranged in front of the virtual camera 2 for photographing the object 1 from respective viewpoints. FIGS. 6A to 6D show concrete examples of effect images. Effect image E01(a) of FIG. 6A shows a state in which, with a central part of the effect image as a generation point, rain is generated radially from the generation point. Effect image E01(b) of FIG. 6B shows a state in which, with an upper part in a center of the effect image as a generation point, rain is generated radially from the generation point. In addition, an effect image E02 of FIG. 6C shows a state in which rain is falling diagonally, and an effect image E03 of FIG. 6D shows a state in which, with a lower part in a center of the effect image as a disappearance point, rain disappears toward the disappearance point. In the first embodiment, the effect image E01(a), E01(b), E02, or E03 shown in FIGS. 6A to 6D is synthesized with respect to the images V1, V2, V3, or V4 shown in FIGS. 4A to 4D to display images as shown in FIGS. 7A to 7F. For example, an image plane V1(a) shown in FIG. 7A shows an image obtained by synthesizing the image V1 of FIG. 4A and the image E01(b) of FIG. 6B. In addition, with respect to the object 1 photographed by the virtual camera 2 arranged between V1 and V2 as shown in FIG. 5, images Va to which an effect processing is applied as shown in FIGS. 8A and 8B are displayed. In this way, in the first embodiment, a corresponding effect image (a texture image for an effective representation) is applied on a plane object consisting of a rectangle two-dimensional model provided in front of the virtual camera 2, the three-dimensional coordinate of the effect image are converted to a two-dimensional coordinate and the effect image after the coordinate conversion is synthesized with a main image so that the effect image of a moving object like rain is displayed. In the image processing for moving rain drops, for example, the texture images of rain drops are moved to predetermined directions by changing the texture images of rain drops in sequence (pattern changing), or by changing the mapping coordinate of the texture image of rain drops in sequence.
FIGS. 9A and 9B schematically show a second embodiment of the conventional effect image processing method. In the case in which “rain” is displayed as an effect image using the above-mentioned small plane objects 4 (see FIG. 2), as shown in FIG. 9A, small plane objects into which an effect image EF is applied as shown in FIG. 9B are arranged in front of the virtual camera 2 for photographing the object 1 from respective viewpoints. In this embodiment, a part of the effect images such as E01(a) or E02 shown in FIG. 6 is drawn for each effect image EF. In the case in which the virtual camera 2 is moved from a position of FIG. 10A to a position of FIG. 10B, the plane objects are rotated such that surfaces of the plane objects face a moving direction of the virtual camera 2 according to the movement of the virtual camera 2. In that case, the plane object of the effect image EF may be moved. In this second embodiment, with respect to the object 1 viewed from the viewpoints on the V1 side, the V2 side, the V3 side, and the Va side (between V1 and V2), a plurality of small plane objects to which effect images are applied as shown in FIGS. 11A to 11D is displayed. In this way, in the second embodiment, a large number of small plane objects rotation and movement of which can be controlled are provided in front of the virtual camera 2, and effect images and a main image are synthesized to display as a display image.
FIG. 12 schematically shows a third embodiment of the conventional effect image processing method. This embodiment is a method of moving the effect image EF as one drop of rain. In this third embodiment, with respect to the object 1 viewed from the viewpoints on the V1 side, the V2 side, the V3 side, and the Va side (between V1 and V2), the effect images EF for one drop of rain moved discretely in a moving direction of the drop of rain and a main image are synthesized to display a display image to which the effect processing is applied as shown in FIGS. 13A to 13D. In this way, in the third embodiment, drops of rain themselves are modeled and an image of each drop of rain and a main image are synthesized to display a display image.